Abstract Detail



Systematics

Ackerfield, Jennifer [1].

Speciation on Sky Islands: The Systematics and Evolution of Cirsium eatonii (“Mountaintop Thistle”).

Cirsium (i.e. “thistles”) is one of the most taxonomically challenging genera of Compositae in North America, particularly in the western states.  This is due largely to convergence, limited morphological differentiation, incipient speciation, and hybridization among taxa.  Within Cirsium, one of the most challenging groups is C. eatonii.  The C. eatonii group is an assemblage of thistles found on “sky islands” of high mountain peaks throughout the Rocky Mountain and Intermountain Regions.  Cirsium eatonii is currently treated as seven infraspecific varieties (var. clokeyi, var. eatonii, var. eriocephalum, var. hesperium, var. murdockii, var. peckii, and var. viperinum) despite being highly polymorphic throughout its range.
Two hypotheses were tested to explain the current biogeographic pattern and diversification of C. eatonii.  First, a common ancestor to C. eatonii occupied lower elevations with a contiguous distribution during the Last Glacial Maximum, and colonization of newly exposed, isolated mountain tops coupled with geographic separation allowed this species to radiate and diversify to the present extent.  Alternatively, multiple, independent colonization events to the alpine ecosystem from two or more lowland progenitors occurred.  Under this hypothesis, C. eatonii would constitute two or more species that have morphologically converged in response to adaptation to similar abiotic conditions.  Phylogenetic analyses using maximum parsimony and maximum likelihood recovered that not only is the C. eatonii group polyphyletic, but many of the currently recognized infraspecific varieties are polyphyletic as well.  Morphological similarity in extant species is likely the result of convergence in response to similar abiotic selective pressures typical of high mountain peaks.  The data are consistent with the recognition of eight distinct species: C. clokeyi, C. eatonii, C. hesperium, C. murdockii, C. peckii, C. scopulorum, and two undescribed species.  Additional work is needed to clarify relationships among C. scopulorum lineages in the Rocky Mountain Region. 


Related Links:
High on Alpine Thistles


1 - Colorado State University, Biology Dept., 1878 Campus Delivery, Fort Collins, CO, 80523, United States

Keywords:
Compositae
Asteraceae
Cirsium
Rocky Mountains
Cirsium eatonii
Sky islands.

Presentation Type: Oral Paper
Number:
Abstract ID:301
Candidate for Awards:None


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